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Formation of High-Pressure Phase of Titanium Dioxide (TiO <sub/>2</sub> -II) Thin Films by Vapor-Liquid-Solid Growth Process on GaAs Substrate
摘要： In this work, the high pressure phase of titanium dioxide (TiO2-II) film is grown with vapor-liquid-solid (VLS) method on <100>-GaAs substrate by utilizing the natural process-induced-strain, originating from the thermo-elastic mismatch between TiO2 and GaAs in VLS process. The mismatches in thermal expansion coefficient and elastic constant of TiO2 and GaAs are Δα (cid:1) 55% and ΔY (cid:1) 170% which incorporate a substantial amount of stress ((cid:1)GPa) during cooling from the growth temperature (500 (cid:3)C). SEM imaging suggests the formation of a continuous film and cross-sectional TEM image confirmed its high crystalline quality. XRD peaks at 2θ ? 31.300 and 58.670 confirm the formation of [111] and [212]-planes of TiO2-II phase and its chemical states are analyzed from X-ray photoelectron spectroscopy (XPS) measurements. The bandgap of TiO2-II phase is estimated to be 2.88 eV from cathodoluminescence study for the first time which agrees satisfactorily with the theoretical predictions reported.
关键词： VLS growth,thin films,process induced-stress,TiO2-II phase
更新于2025-09-23 15:21:21
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Analytical Modeling of Residual Stress in Laser Powder Bed Fusion Considering Parta??s Boundary Condition
摘要： Rapid and accurate prediction of residual stress in metal additive manufacturing processes is of great importance to guarantee the quality of the fabricated part to be used in a mission-critical application in the aerospace, automotive, and medical industries. Experimentations and numerical modeling of residual stress however are valuable but expensive and time-consuming. Thus, a fully coupled thermomechanical analytical model is proposed to predict residual stress of the additively manufactured parts rapidly and accurately. A moving point heat source approach is used to predict the temperature ?eld by considering the e?ects of scan strategies, heat loss at part’s boundaries, and energy needed for solid-state phase transformation. Due to the high-temperature gradient in this process, the part experiences a high amount of thermal stress which may exceed the yield strength of the material. The thermal stress is obtained using Green’s function of stresses due to the point body load. The Johnson–Cook ?ow stress model is used to predict the yield surface of the part under repeated heating and cooling. As a result of the cyclic heating and cooling and the fact that the material is yielded, the residual stress build-up is precited using incremental plasticity and kinematic hardening behavior of the metal according to the property of volume invariance in plastic deformation in coupling with the equilibrium and compatibility conditions. Experimental measurement of residual stress was conducted using X-ray di?raction on the fabricated IN718 built via laser powder bed fusion to validate the proposed model.
关键词： residual stress prediction,IN718,additive manufacturing,experimental measurement of residual stress
更新于2025-09-23 15:21:01
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Waveguide optimization and its evaluation of a doped polymer optical ???ber designed for visual detection of stress
摘要： A fiber-optic strain sensor using a fluorophore-doped polymer optical fiber (POF) was fabricated at various waveguiding conditions. The effects attributed to each structural feature of the sensor were characterized by observing the sensor?s response. Two fluorophores, Coumarin 540A and Rhodamine 6G, were used to dope the core and the cladding of a poly(methyl methacrylate)-based POF, respectively. Using doped POFs with different numerical apertures (NAs), the changes in the fluorophore peaks upon the application of stress were analyzed by applying macrobending (s) to the fiber. Although the sensor response did not show linearity with respect to the NA, it was found that the shape of the Coumarin 540A-attributed peak was a factor that represented the sensor?s sensitivity. As a result, the double-cladding structure demonstrated its effectiveness in improving the stress sensitivity.
关键词： double-cladding structure,fluorophore-doped,polymer optical fiber,numerical aperture,fiber-optic strain sensor,stress sensitivity
更新于2025-09-23 15:21:01
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Measurement of Weld Zone Properties of Laser-Welded Tailor-Welded Blanks and Its Application to Deep Drawing
摘要： Weld zones in tailor welded blanks have different mechanical properties than the base metals and thus have significant effects on formability. In this work, flow stresses of weld zones in laser-welded dissimilar dual-phase steels were measured. Strains at the weld zones of notched specimens were measured using the digital image correlation method and the flow stress data were corrected considering the anisotropy. For validation, finite element simulations were performed for the cup drawing process by considering the measured weld zone properties, and the weld line movements were compared with the measurements.
关键词： Laser welding,Formability,Digital image correlation,Dual-phase steel,Flow stress
更新于2025-09-23 15:21:01
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Stress-Controlled Frequency Tuning and Parametric Amplification of the Vibrations of Coupled Nanomembranes
摘要： Noninvasive tuning of the mechanical resonance frequencies of suspended parallel nanomembranes in various monolithic arrays is achieved by piezoelectric control of their tensile stress. Parametric amplification of their thermal fluctuations is shown to be enhanced by the piezoelectric actuation and amplification factors of up to 20 dB in the sub-parametric oscillation threshold regime are observed.
关键词： nanomembrane resonators,piezoelectrical actuation,parametric excitation,stress engineering
更新于2025-09-23 15:21:01
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Conditioned media from blue light-emitting diodea??exposed fibroblasts have an anti-inflammatory effect in vitro
摘要： We have previously reported the protective effects of blue light-emitting diode (BLED)–stimulated cell metabolites on cell injury. To further examine the effect of conditioned media (CM) derived from BLED (5 J/cm2)-exposed human normal fibroblasts (CMBL5) for clinical application, we have used the choline chloride and phenol red–free media and then concentrated CMBL5 using a centrifugal filter unit. The collected CMBL5-lower part (CMBL5-LO) has evaluated the inflammatory protein expression profile in LPS-stimulated RAW264.7 cells. Comprehensive metabolomic profiling of CMBL5-LO was carried out using hybrid tandem mass spectrometry. Treatment with CMBL5-LO showed the cytoprotective effect on apoptotic cell death, but rather increased apoptotic cells after treatment with CMBL5-upper part (CMBL5-UP). In addition, CMBL5-LO inhibited several chemo-attractants, including interleukin (IL)-6, macrophage inflammatory protein (MIP)-2, chemokine (C-C motif) ligand 5 (CCL5), granulocyte colony-stimulating factor (GCSF), and monocyte chemoattractant protein-1 (MCP-1) expression. Pro-inflammatory nitric oxide was decreased after CMBL5-LO treatment, but not by CMBL5-UP treatment. Interestingly, treatment with CMBL5-LO stimulated expression of heme oxygenase-1, indicating its anti-inflammatory property. Most endoplasmic reticulum (ER) stress proteins except for transcription factor C/EBP homologous protein (CHOP) were highly expressed after irradiation with BLED in cells. Further studies are needed to examine the precise mechanism by CMBL5-LO in cells.
关键词： Inflammation,CMBL5-LO,Light-emitting diode,ER stress
更新于2025-09-23 15:21:01
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Effect of Static Magnetic Field on the Evolution of Residual Stress and Microstructure of Laser Remelted Inconel 718 Superalloy
摘要： As a typical additive manufacturing technique, direct energy deposition is restricted from further application due to the presence of residual stress and the structural deformation. Thus, minimizing the residual stress plays a crucial role in additive manufacturing. In this work, a transverse static magnetic field is introduced in the laser remelting of Inconel 718 superalloy to investigate the effects on residual stress and microstructural change. The x-ray diffraction technique was used to examine the residual stress variation. Optical microscope and scanning electron microscope were applied to observe the microstructure evolution. It was found that the compressive residual stress of the remelted region was notably reduced from 392.50 to 315.45 MPa under the effect of the magnetic field of 0.55 T. Furthermore, it was observed that the average dendrite spacing was reduced by about 32% under the magnetic field. During the laser remelting process, the imposed electromagnetic force minimized the flow field within the molten pool, inhibiting the heat transfer and minimizing the cooling rate. These directly reduced the residual stresses. Based on research findings, the magnetic field can be a potential method to eliminate the residual stress in laser additive manufacturing components.
关键词： laser direct deposition,static magnetic field,Inconel 718 superalloy,laser remelting,residual stress,thermoelectric magnetic force
更新于2025-09-23 15:21:01
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Gradient microstructure and vibration fatigue properties of 2024-T351 aluminium alloy treated by laser shock peening
摘要： To investigate the improvement in vibration fatigue and the strengthening mechanism of laser shock peening, a nanosecond laser was used to strengthen the 2024-T351 aluminium alloy. Accordingly, the microstructure, residual stress, nanohardness and surface roughness of the treated alloy were measured. Subsequently, the vibration fatigue damage and fatigue life were evaluated, and the vibration fracture morphology was observed. The results showed that the grains in the peened surface were re?ned. A residual stress of ?141 MPa and a nanohardness of 3.1 GPa were obtained by laser shock peening. Based on the relationship between the peened microstructure and fracture morphology, it was deduced that an increase in the grain boundaries led to a lower crack initiation rate and a higher crack initiation life. The compressive residual stress decreased the crack growth rate and increased the crack growth life. Therefore, laser shock peening increases the total vibration fatigue life by about 63.5%.
关键词： Laser shock peening,Vibration fatigue,2024-T351 aluminium,Compressive residual stress,Microstructure
更新于2025-09-23 15:21:01
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Residual stress analysis of thin film photovoltaic cells subjected to massive micro-particle impact
摘要： Residual stresses play a crucial role in both light-electricity conversion performances and the lifespan of photovoltaic (PV) cells. In this paper, the residual stress of triple junction cells (i.e. GaInP/GaInAs/Ge) induced by laser-driven massive micro-particle impact is analyzed with a novel method based on backscattering Raman spectroscopy. The impact process, which induces damage to the PV cells and brings the residual stress, is also investigated by optical microscopy (OM) and Scanning Electron Microscopy (SEM). The results show that the PV cells would exhibit various damage patterns. At the same time, strong residual stresses up to hundreds of MPa introduced in the damaged PV cells after impact have been analysis, providing an effective perspective to better understand the damage behavior and residual stress features of PV cells during their service life.
关键词： Damage behavior,Residual stress,Photovoltaic cells,Micro-particle impact,Raman spectroscopy
更新于2025-09-23 15:21:01
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The effects of laser peening on laser additive manufactured 316L steel
摘要： Laser peening has an extensive application in traditional manufacturing industry. However, in additive manufacturing, the initial stresses on the parts often reduce the effects of laser peening and make it hard to achieve a desirable residual stress distribution. In this investigation, the interaction of initial residual stress and laser peening-induced stress was studied through numerical simulation and experimental tests. A finite element model (FEM) model was built to predict the stress distribution on laser-deposited sample, and its changed state is affected by laser peening. The microstructure and mechanical properties were also characterized experimentally. The result turned out that the thermal-induced tensile residual stress in laser-deposited sample can affect the laser peening result in both horizontal and longitudinal directions. Some mechanical properties of the LAMed sample were changed after LSP treatment. The hardness on the surface and 1-mm depth have been increased by 7% and 22%, respectively, and the yield strength was increased by 16%, while there is no significant change in the tensile strength and elongation rate.
关键词： Finite element analysis,Laser peening,Laser additive manufacturing,Residual stress
更新于2025-09-23 15:21:01